1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method of the same, and aims at a structure and a forming method of an insulation film, in particular, a silicon nitride (SiN) film to be disposed on a surface of a semiconductor, in particular, a compound semiconductor region for high-power output.
2. Description of the Related Art
In a semiconductor device, in particular, in a compound semiconductor device used for high-power output, a pair of ohmic electrodes and a gate electrode are formed on a surface of a compound semiconductor region whose active region is defined by a method such as ion implantation. Further, a protective insulation film made of a silicon nitride film or the like is formed in a manner to cover the surface of the compound semiconductor region and the ohmic electrodes.
A performance of the compound semiconductor device largely depends on a state of an interface between the surface of the compound semiconductor region and the protective insulation film and on a property of the protective insulation film itself. This is due to chemical and physical weakness of a surface state of the compound semiconductor. Particularly, in a semiconductor device for high-power, stability of the surface state is important. Research organizations have heretofore performed and are still performing many investigations about a good insulation film for surface protection and a matching property between a device surface and the insulation film.
(Patent Document 1)    Japanese Patent Application Laid-open No. 2001-77127
Performances required of the protective insulation film, particularly a SiN film, for protecting the surface of the compound semiconductor region are a stabilization action for the surface of the compound semiconductor region and a good insulation characteristic of the protective insulation film itself. The stabilization action for the compound semiconductor region indicates an action to restrict a chemical change phenomenon of the surface and to restrict a change in a surface electric potential due thereto by forming an insulation film layer on the surface. The good insulation performance of the protective insulation film itself indicates a state that a leak current flowing in the film is scarce even at a time of application of a higher field. In the SiN film, in particular, a leak current in the film largely changes depending on chemical bonding states of atoms of silicon (Si) and nitride (N).
For example, the insulation film superior in stabilization action for the surface of the compound semiconductor region indicates an insulation film including a lot of hydrogen (H) terminated bonds and the like in the film. Such an insulation film has a substantial chemical action for the surface of the compound semiconductor region, and depending on circumstances, there is expected an action to bring back an unstable atomic bonding state existing on the surface to a normal state. Chemical unstableness of the surface of the compound semiconductor region leads to a current fluctuation at a time of device operation and to a reduced reliability. The insulation film having the good insulation performance of the film itself indicates an insulation film which has no free bond hands in the film. In the insulation film as above, a current flowing in the film is minute, so that a leak current through the film can be restricted and a change in film quality due to electric conduction in the film can be mitigated. In other words, a reliability of a compound semiconductor device is improved.
As described above, it is inherently difficult to achieve both of the improvement of the chemical stability on the surface of the compound semiconductor region and the good insulation performance of the insulation film itself, in view of chemical bonding of the protective insulation film.